I\'m working on putting together a liquid style-sheet and it works wonderful. One thing that I\'ve noticed is that my browser window in Chrome won\'t resize below 400px it j
I like this tool because it lets you switch quickly and also switches between portrait/horizontal easily for mobile sizes. It also allows you to make a personalized bookmark let, so if you design for obscure resolutions frequently, you can save them and use them.
I had to use one of these tools because even with the above answer I couldn't get my window to scale to 320 properly, this tool seems to be a faster solution overall.
http://lab.maltewassermann.com/viewport-resizer/